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La pompe à paire de Cooper, un read-out pour le Qubit Josephson

Abstract : The superconducting double island consists of three Josephson junctions in series, which can be
used as a two levels system. The energies of the quantum macroscopic states are controlled by two gate voltages and by one bias voltage VB.
The transfer of one Cooper pair through the circuit involves incoherent transitions transferring
2eVB of energy to the electromagnetic environment, corresponding to the bias voltage. The transport
properties through this device, in absence of quasiparticles poisoning, show the competition between
the coupling of degenerate states of the double island and the relaxation rate, depending on the
bias voltage. If the relaxation is the bottle neck for the transport, the resulting current is proportional
to the relaxation, leading to a quantum regime. On the other hand, if the coupling becomes the limiting factor (or if the relaxation dominates), the dynamic changes and the current decreases paradoxically, leading to
a Zeno regime. At low enough bias voltages, the supercurrent is identified through the three junctions
in series.
Finally, the effect of an adiabatic evolution is examined. The adiabatic evolution is realized by means
of two alternative 90° shifted gate voltages, leading to a direct pumping current through the circuit. The
thesis shows how the adiabatic pumping can be used to read out the state of the system. The pumping
current is actually sensitive to the occupation of the quantum state, the sign of the pumped charge in
the ground and the first excited state being opposite.
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Contributor : David Schaeffer <>
Submitted on : Wednesday, January 4, 2006 - 9:04:14 PM
Last modification on : Thursday, January 11, 2018 - 6:14:42 AM
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  • HAL Id : tel-00011227, version 1




David Schaeffer. La pompe à paire de Cooper, un read-out pour le Qubit Josephson. Matière Condensée [cond-mat]. Université Joseph-Fourier - Grenoble I, 2005. Français. ⟨tel-00011227⟩



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